Targeted and Systematic Approach to the Study of p<i>K</i>_a Values of Imidazolium Salts in Dimethyl Sulfoxide

A range of more than 25 imidazolium salts, chosen for their differing steric and electronic features, were prepared, and their pKa values were determined using the bracketing indicator method. Through the systematic change in the structure of the imidazolium cation, the effect of varying substituents at each position on the heterocyclic ring was determined; particularly, the transmission of electronic effects was quantified using Hammett parameters. These new data give an indication of the strength of base required for deprotonation and the potential to correlate these data with the nucleophilicity of the corresponding carbenes.本研究制备了25余种具备差异化空间位阻与电子特性的咪唑鎓盐（imidazolium salts），并采用指示剂夹心法（bracketing indicator method）测定了其pKa值。通过系统性调控咪唑鎓阳离子的结构，明确了杂环各位置取代基变化所产生的影响；尤为关键的是，借助哈米特参数（Hammett parameters）量化了电子效应的传递过程。本次实验获得的全新数据可为去质子化所需的碱强度提供参考依据，同时有望将这些数据与对应卡宾的亲核性建立关联。